A bobbin thread winder which is mounted in a sewing machine includes a drive wheel coming in contact with a drive pulley equipped on an upper shaft of the sewing machine at an outer periphery thereof, a thread winding shaft rotating integrally with the drive wheel, a rotating arm rotatably supporting the thread winding shaft, a thread winding lever which is circumscribed the thread wound around a bobbin set in the thread winding shaft, a cam member rotating coaxially with the thread winding lever, and a cam follower which has a recessed portion to which a protrusion of the cam member is fitted and is integrally connected with the rotating arm (for example, see Japanese Unexamined Patent Application Publication No. 2008-29381).
In the above-described bobbin thread winder, a torque is transmitted from the upper shaft of the sewing machine to the bobbin set in the thread winding shaft through the drive pulley and the drive wheel. When the thread is wound around the bobbin, the thread winding lever gradually rotates in accordance with the winding amount. When the winding amount reaches a prescribed amount, the protrusion of the cam member is fitted to the recessed portion of the cam follower, the cam follower and the rotating arm rotate, and then the drive wheel is separated from the drive pulley, whereby the thread winding is finished.
However, the above-described bobbin thread winder merely uniformizes the outer diameter of the thread wound around the bobbin.
Therefore, since the winding amount of the thread wound around the bobbin varies depending on the type and thickness of the bobbin thread, it is not possible to grasp the winding amount of the bobbin thread accurately.